Optical emission spectroscopy of point-plane corona and back-corona discharges in air |
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Authors: | T Czech A T Sobczyk A Jaworek |
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Institution: | 1.Institute of Fluid Flow Machinery,Polish Academy of Science,Gdańsk,Poland;2.Institute of Physics,Pomeranian Academy,S?upsk,Poland |
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Abstract: | Results of spectroscopic investigations and current-voltage characteristics of corona
discharge and back discharge on fly-ash layer, generated in point-plane electrode geometry
in air at atmospheric pressure are presented in the paper. The characteristics of both
discharges are similar but differ in the current and voltage ranges of all the discharge
forms distinguished during the experiments. Three forms of back discharge, for positive
and negative polarity, were investigated: glow, streamer and low-current back-arc. In
order to characterize ionisation and excitation processes in back discharge, the emission
spectra were measured and compared with those obtained for normal corona discharge
generated in the same electrode configuration but with fly ash layer removed. The emission
spectra were measured in two discharge zones: near the tip of needle electrode and near
the plate. Visual forms of the discharge were recorded with digital camera and referred to
current-voltage characteristics and emission spectra. The measurements have shown that
spectral lines emitted by back discharge depend on the form of discharge and the discharge
current. From the comparison of the spectral lines of back and normal discharges an effect
of fly ash layer on the discharge morphology can be determined. The recorded emission
spectra formed by ionised gas and plasma near the needle electrode and fly ash layer are
different. It should be noted that in back arc emission, spectral lines of fly ash layer
components can be distinguished. On the other hand, in needle zone, the emission of high
intensity N2 second positive system and NO
γ
lines
can be noticed. Regardless of these gaseous lines, also atomic lines of dust layer were
present in the spectrum. The differences in spectra of back discharge for positive and
negative polarities of the needle electrode have been explained by considering the kind of
ions generated in the crater in fly ash layer. The aim of these studies is to better
understand the discharge processes encountered in electrostatic precipitators. |
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